This invention relates generally to sensors and airfoils useful for various types of engines and other apparatus, and more particularly to sensors integrated into vanes.
Sensors typically include two basic structures. One of these structures is an element that measures a physical attribute of interest, such as temperature or pressure, and that also provides a useful signal in either an electrical or other physical form. The other structure is an external body that simultaneously mounts, supports, and protects the sensing element. This two-part configuration allows the entire sensor to be removed and replaced independently of other local hardware in, for example, an aircraft.
Some sensors are immersed in an environment of flowing fluids that have highly dynamic secondary properties (such as one or more of pressure, temperature, turbulence, conductivity, directional vector, etc.). The design of the external supporting structure of such sensors relative to the sensing element can significantly affect the accuracy and the time constant of measurements made by that element.
Typically, a supporting body of a sensor is not intended to perform vane-vectoring effects on a flow stream. Instead, sensors are designed to induce as little and as neutral an effect as possible on a flow stream. The depth of immersion of a sensor and the width and shape of its body should be designed to minimize induced effects on the flow stream. Also, the sensor should be made only large enough for durability and to reach the particular zone of interest having the physical property to be measured. A potentially steep tradeoff exists between measuring attributes of a flowstream, interfering with the flowstream itself, and sensor strength and reliability. Thus, mounting a separate sensor in a flowstream can have a significant negative effect on the flowstream itself. For example, at least one known prior art assembly includes a sensor mounted at a separate, cantilevered body near the top of a vane. Such standalone-type sensors add their own turbulence and blocking to an air stream, requiring an increase in air flow speed to make up for the reduction in flow area.
A sensor element that is integrated into an airfoil or other fluid flow vane is typically mounted and configured in one of the following three ways:
(1) The sensor is enclosed inside the flow vane body, with or without aspiration holes in the walls of the flow vane. Holes allow a portion of the flow stream to enter inside the flow vane cavity to reduce the signal response time constant or increase accuracy of the sensor measurement. Enclosing a sensor in the body of a flow vane always results in the sensor signal having a longer time constant than that of an unenclosed sensor. This longer time constant can be shortened only by modifications in the flow vane that sacrifice flow vane strength and integrity, such as aspiration holes or thinning a wall dimension to reduce the bulk mass of the flow vane. The radiant temperature of the flow vane body surrounding the sensor affects the sensor element time constant, or in case of pressure, the size of the aspiration holes will affect the pressure rate of change. This configuration may not be effective in an application with highly dynamic secondary properties as described above.
(2) The sensor protrudes from walls of a body element of the flow vane. In this configuration, the sensor element protrudes into the flow stream from the normal flow vane element, which is defined here as a projection of a cross section of the flow vane along an axial length with very low or no profile discontinuity features. This cantilevered sensor configuration allows a quarter wave primary vibration response. It is difficult or impossible to remove or install the sensor intact in this configuration without making the sensor flexible. However, it may not be desirable for a sensor to be flexible in a very hot and/or fast flow stream environment, as durability of the exposed portion of the sensor may be reduced. Axial removal of the flow vane is also complicated by protrusion of the sensor element, which is typically mounted substantially orthogonal to a wall surface of the flow vane.
(3) The sensor is applied directly to the skin of the flow vane body walls. In this case, an already planned and optimized flow vane design may not require extensive modification. However, the exposed sensor body can disrupt airflow over the entire length of the sensor lead element. A strong tradeoff exists between reliability and the magnitude of the disruption of the primary flow because more reliable sensors are larger in size and more likely to disrupt the primary flow. Usually, this configuration is used in development studies due to low sensor reliability. In addition, vane removal may be difficult due to the external modification.
Although each of these sensor configurations provides adequate sensor information, it is clear that the tradeoffs involved for each may not be desirable for particular sensor/vane flow measurement applications. For example, these configurations may not minimize airflow disruption while simultaneously maintaining or improving reliability and time constant of either the sensor element or of the flow vane.